Considering a Rotary conversion, need help

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dave2336

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Feb 28, 2011
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fort smith,ar
I'm just afraid of getting detonation and blowing the whole thing up if I were to have a wastegate failure or something similar.
If your going with the Megasquirt ECU you program over boost protection. You can pull fuel and spark as the boost level get too high. That said, I've never looked at the existing Megasquirt software for rotaries. But, if it doesn't exist just program it.
 

DLrocket89

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Janesville, Wi
I'll stop short of calling that impossible but I have a couple problems with this failure. First, I doubt such a failure would be immediate and without warning that the pilot didn't have time to throttle down the engine.

Even allowing that it was a sudden failure and the engine "exploded" before he had time to reach for the throttle the laws of physics dictate that increased boost will result in increased power and such power results in acceleration and the propeller would be going a lot faster. This is where the RPM limiter of the ECU would kick in and automatically cut power to the engine preventing the blow out.

Lastly, any decent ECU has overboost protection which if programmed will cut power if such a condition is detected.

In conclusion I call bollocks.
Good analysis. *shrugs* I try to have a reasonably good BS filter when I'm reading things on the internet. Perhaps this got through?
 

DLrocket89

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If your going with the Megasquirt ECU you program over boost protection. You can pull fuel and spark as the boost level get too high. That said, I've never looked at the existing Megasquirt software for rotaries. But, if it doesn't exist just program it.
1) Yes, they do boost control with it, you can map out your boost level by RPM, throttle position, and MAP.
2) It's been done on several rotaries. No worries. It uses a 36-2-2-2 wheel and (I think) because the rotors are three sided and turn at 1/3 the Eshaft rotational speed, the plugs fire in the same spot each time around the wheel (forgetting about advance and whatnot).
3) FWIW, the MS also does things like ignition/fuel cut if things get out of hand.
 
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It's not complex installing a wastegate, or better still buying a turbo with the systembuilt in. Simply set it to the desired manifold pressure and it will bleed off the surplus pressure without the pilot so much as being aware of it. It is an idiot-proof system.
 
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If you cannot control it mechanically, do not panic. Be what you were trained to do, fly aircraft and in so doing manage the power settings. There is nothing that is going to explode in your face like crackers at a kids party. When you apply power, keep an eye on your manifold pressure while increasing power. There is no magic to applying power whether it be in a car, an aircraft, a boat or a borehole pump at your country escape. Watch the guage as you open the throttle until you get the desired boost, take your feet off the foot brakes and accelerate to to the big blue. If you must apply power for a go around, slowly increase power over a period of one or two seconds. Do not thump the throttle open from one extremem to another. Treat it as lovingly as you bride on the day you married and she'll treat you well. I second or two's delay will not kill you. It could save your life. Stop applying power two inches before the desired power setting to give the turbo time to catch up. Check it again every ten seconds to make fine adjustments if necessary. No turbo will pack uo from a thirty second overboost unless you chose the wrong turbo in the first place and assisted it with a stick of dynamite. Lastly, read what Craig has to say about Wankel motors on www.tripd.com He tells us when an Wankel fails, it is unlike a psiton motor that stops immediately. According to him, Tracy Cook and Paul Lamar, the motors will usuall keep working for long enough for you to find an airfield.
 

EzyBuildWing

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Sep 23, 2009
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Sydney NSW Australia
Hear! Hear!
Hi Guys.....cheapest flying Wankel is a "blown" 13B engine direct-driving a prop bolted directly onto end of the crankshaft. Propeller and blower-speed optimized for 3000 rpm continuous...power-output approx 150hp easy, with turbine-smoothness. This engine with a Rotrex blower would be far more reliable and much tougher(bullet-proof) than ANY currently-available aviation powerplant...and at a fraction of the cost! Only mod would be a thrust-bearing. Duncan Aviation(Oklahoma) offered a similar engine some years ago....it was awesome! Lightweight Rotrex blower uses simple rolling-elements and NOT toothed-gears...simpler and cheaper and NO teeth to wear.

So what's the ideal airplane for such a magnificently-simple and bulletproof inexpensive engine?

How about a Breezy with "DoubleEnder" STOL wings? For low/slow smooth fun-flying and sight-seeing, it would be unbeatable!
 

rv7charlie

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Hi Guys.....cheapest flying Wankel is a "blown" 13B engine direct-driving a prop bolted directly onto end of the crankshaft. Propeller and blower-speed optimized for 3000 rpm continuous...power-output approx 150hp easy, with turbine-smoothness. This engine with a Rotrex blower would be far more reliable and much tougher(bullet-proof) than ANY currently-available aviation powerplant...and at a fraction of the cost! Only mod would be a thrust-bearing. Duncan Aviation(Oklahoma) offered a similar engine some years ago....it was awesome! Lightweight Rotrex blower uses simple rolling-elements and NOT toothed-gears...simpler and cheaper and NO teeth to wear.

So what's the ideal airplane for such a magnificently-simple and bulletproof inexpensive engine?

How about a Breezy with "DoubleEnder" STOL wings? For low/slow smooth fun-flying and sight-seeing, it would be unbeatable!
Any examples of an actual flying a/c using a supercharged direct drive Mazda rotary at 3k rpm?
 

rv7charlie

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I do know of one supercharged Renesis flying on an RV-10, but he's seriously considering a switch to turbo for efficiency reasons.

My bigger question was about *direct drive* working with a rotary. Maybe there are some 'down under', but I've been following rotary a/c for a long time (installing one in my RV-7 now), and I've never heard of anyone even trying it. Here's a set of power curves for a stock and highly modified 3rd gen turbo RX-7 car.
http://www.rx7club.com/attachments/time-slips-dyno-121/476750d1348451646-stock-power-curve-fd_stock_vs_single.jpg
The stock HP is around 60 at 3k rpm. Even highly modified, it's still only around 120 HP at 3k rpm. Pushing boost enough to make 150 HP at that rpm sounds like a huge risk of detonation, even in a rotary. My Renesis FWF weighs ~310 lbs, dry, without a turbo. Add turbo & plumbing & swap the redrive for an external bearing/shaft/thrust bearing & weight might even grow a bit; pretty high for 150 HP.

I'd love to hear about any a/c that are flying with a DD rotary

Charlie
 

rv7charlie

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That list is at least a decade out of date; many on that list are no longer flying, & I'm confident that there are quite a few flying who aren't on the list. All that I'm aware of are using some version of a psru.
 

Lucrum

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I don't claim to be a Rotary expert, even though I have overhauled a 20B. But it's my understanding the rotary is far better suited to turbochargers than super chargers
 

rv7charlie

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That's because they are internal combustion engines, used in an environment that needs fuel efficient power production far more than instant throttle response. :)
 

rv6ejguy

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Most aircraft engine applications are better suited to turbocharging for many reasons. The potential problem with turbos and Wankels is that the high EGTs may tax the turbine wheel/ housing/ rear bearing thermally in continuous operation. Most are rated for a max of 1650F. I've run Reno racers to 1800F for short periods but that's pretty scary.
 

narfi

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Something that does seem lacking on the web is any concrete data on "best" or "standard" setups for aircraft conversions.

Lots of engine mod sites out there and lots of racers and "hobbiests" taking these engines to all sorts of crazy power, but no real history behind lifespan or reliability at set outputs.

What kind of lifespans are you looking at for a P ported or turboed 13B to 300hp? I would assume not great, but no real info seems to be out there.

It is a topic I know very little about but it does interest me for two reasons.

1. Great power to weight ratio seems great for a homebuilt plane, cheaper to buy cheaper to overhaul, more expensive for the original firewall forward setup?

2. Great power to weight ratio and efficient at higher rpm? Potential as a 'range extender' for an electric powered homebuilt?

Once you have the PSRU, exhaust, radiator, prop, etc.... all mounted firewall forward, what is the actual weight differences between these setups and a certified aircraft engine at similar power outputs? (o200 or rotax 912/914 vs stock 13B.... or moded to 300hp vs the io550?) I realize there are a lot of variables, but am curious for an honest unbiased comparison between the different setups.

Is there any info out there for rotaries being used as light weight generators? Or is that still a pipe dream?
 
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Vigilant1

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The potential problem with turbos and Wankels is that the high EGTs may tax the turbine wheel/ housing/ rear bearing thermally in continuous operation. Most are rated for a max of 1650F. I've run Reno racers to 1800F for short periods but that's pretty scary.
But the turbo turbine sections used on the "stock" Mazda cars get good longevity, right? I'd think for aircraft use we'd be looking at a different compressor (to match better with the higher density altitudes at which aircraft typically operate compared to cars).
There's so much thermal and kinetic energy in a rotary exhaust that the problem is taming it, I guess. Seems a shame that the waste energy can't be put to practical use to do a lot of things on an airplane--e.g. improve induction, make electrical power, pressurize a cabin, even go back to the propshaft mechanically in a turbocompound setup (Paul Lamar has been on the turbocompound hunt for a long time). As a bonus, it can eliminate the need for a heavy and trouble-prone muffler.
 

rv6ejguy

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But the turbo turbine sections used on the "stock" Mazda cars get good longevity, right? I'd think for aircraft use we'd be looking at a different compressor (to match better with the higher density altitudes at which aircraft typically operate compared to cars).
There's so much thermal and kinetic energy in a rotary exhaust that the problem is taming it, I guess. Seems a shame that the waste energy can't be put to practical use to do a lot of things on an airplane--e.g. improve induction, make electrical power, pressurize a cabin, even go back to the propshaft mechanically in a turbocompound setup (Paul Lamar has been on the turbocompound hunt for a long time). As a bonus, it can eliminate the need for a heavy and trouble-prone muffler.
I used to rebuild turbos for a living. Saw enough problems on Wankel ones with relatively low time to know they didn't mix that well. I helped a some guys match proper ones for airplanes years back after they failed a couple stock ones in a matter of a few hours and one experimenter scattered the engine twice. I doubt if any single turbo Wankel powered aircraft has got 500 hours on the engine or turbo yet without coming out of the airplane at least once or twice. If anyone does, I'd be interested in hearing about the details and experience with it.

Paul Lamar has lots of ideas, rarely actually builds and flies any of them himself. He certainly will never be running a turbocompound Wankel any time soon.

Any IC engine has massive amount of energy in the exhaust stream- enough to blow the strongest engine ever built to bits with a turbo. That's not the goal in aircraft though, we need reliability. I'm a big fan of turbos in aircraft if done right. Problem is most people don't have a clue and break stuff. The hot section on stock auto turbos is completely wrong for the aviation application and often the compressor is too to a lesser extent usually. Anyway, done right, it works really well on piston engines and can on Wankels too. Have to watch the EGTs though if you want longevity.

+1 on the noise thing, the turbo can take a ton of bark out of the Wankel note.
 

rv6ejguy

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Jun 26, 2012
Messages
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Location
Calgary, Alberta, Canada
Something that does seem lacking on the web is any concrete data on "best" or "standard" setups for aircraft conversions.

Lots of engine mod sites out there and lots of racers and "hobbiests" taking these engines to all sorts of crazy power, but no real history behind lifespan or reliability at set outputs.

What kind of lifespans are you looking at for a P ported or turboed 13B to 300hp? I would assume not great, but no real info seems to be out there.

It is a topic I know very little about but it does interest me for two reasons.

1. Great power to weight ratio seems great for a homebuilt plane, cheaper to buy cheaper to overhaul, more expensive for the original firewall forward setup?

2. Great power to weight ratio and efficient at higher rpm? Potential as a 'range extender' for an electric powered homebuilt?

Once you have the PSRU, exhaust, radiator, prop, etc.... all mounted firewall forward, what is the actual weight differences between these setups and a certified aircraft engine at similar power outputs? (o200 or rotax 912/914 vs stock 13B.... or moded to 300hp vs the io550?) I realize there are a lot of variables, but am curious for an honest unbiased comparison between the different setups.
There were twin Wankel RV8s a number of years back. One was flight tested at the Van's factory against the Lycoming powered demonstrator. Was a bit heavier, climbed a bit better, went a bit faster and burned a bit more fuel. They had custom cowlings, eliminating the side cheeks, with a nice inlet under the spinner. Looked very cool.

http://www.wrathall.com/Mustang/build log/240/240 index.html

Wankels (13Bs) are much heavier than a 912 Rotax but also put out at least 50% more hp so not really in that class. More comparable to Lycoming 360 or similar.
 
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